The invention relates to the performance of surgery upon the anterior surface of the cornea, in order to change the anterior-surface profile and thereby change the optical performance of a given eye, via in vivo surgery.
Radial keratotomy (RK) is the term currently used to describe such a procedure, for the case of plural slits cut at spaced locations about the optical axis of the eye, and cut to a depth that is (a) less than the thickness of the cornea and (b) in an annular region which is outside the optical zone, i.e., outside the optically used central region of the cornea. The result is to circumferentially weaken and thus to allow the front-surface curvature of the optically used region to flatten, in reduction of a myopic condition or in reduction of an astigmatic condition (AK), depending upon the symmetry of cut distribution, or upon the orientation of the asymmetry of cut distribution, as the case may be.
To date, an accumulation of data and experience exists from which to enable the ophthalmic surgeon to predict, with some degree of reasonable approximation, the number, the depth, and the distribution of cuts to be made in order to approximate a desired optical correction, to the extent that the patient quickly is aware of an improvement in his eyesight, following RK surgery. And suppliers of ophthalmic tools and instruments have refined their offerings in recognition of the need for precision in what remains essentially a manual operation. For example, Katena Products, Inc. of Denville, N.J., devotes a double-page spread in its current catalog, "Katena Diamond Knives", to the listing, diagramming and description of six different kinds of diamond micrometer knives, specifically for use in RK surgery and/or AK (astigmatic keratotomy) surgery. Each knife is equipped with a footplate for sliding reference to the corneal epithelium in the course of making a cut, and a micrometer scale is associated with axial-displacement mechanism in the knife handle to enable precise setting of the extent to which the cutting end of the knife is to project beyond the front surface of the footplate. Such settings are adjustable in 10-micron increments, from 0 to 1.5-mm, and a special gauge enables the surgeon to double-check whether the setting is precisely what was intended via the micrometer adjustment.
However, with all the precision and quality of cut that can be made with such a fine knife instrument, the fact remains that it is the surgeon upon whom ultimate reliance must be placed, because radial and astigmatic surgical procedures continue to be hand operations.
Among the further currently available instrumentation in aid of RK and AK keratotomies are the various marking instruments whereby to mark the patient's cornea, in identification of one or more features, including the visual-axis intercept, the optically used central area (i.e., the optic zone), a T-incision marker with a succession of blade-length offerings, an astigmatism marker, a helicoidal marker, and a hexagon open-pattern marker. These and other marker products are shown in another Katena Products catalog, "Instruments for Radial and Astigmatic Keratoplasty". Again, however well the cornea may have been marked for surgery, the fact remains that the final quality of a given operation rests entirely on the manual skill of the ophthalmic surgeon, in that all marker instruments must be out of the way while the manual operation proceeds.